It is well known that exteroceptive factors such as environmental influences, certain sensory inputs, etc., reach the hypothalamus by way of a neural-hormonal pathway and influence ovulation and cycle regularity in man and other primates. However, little is known of the connection between the exteroceptive input and its pathways, and the neuroendocrine regulation of ovulation. Studies based on rats indicate (1) the basomedial hypothalamus regulates the release of gonadotrophin by influence of the anterior hypothalamus, including medial preoptic area, (2) the estrahypothalamic region, such as limbic area or midbrain, also has an influence upon the hypothelamic regulation of ovulation. Significant differences in the effect of light and other sensory inputs between rodents and primates indicate that the regulatory mechanism in the rat may not be identical with that operative in the nonhuman primate or man. It is, therefore, important to know whether the dynamics of the regulatory system, as seen in the rat and Rhesus monkey, represent a general biological phenomenon, or whether important parts thereof are solved in various ways by different species. By electrophysiological monitoring of neural activity and measurement of endocrine parameters, and immunohistochemical determination of the LHRH secretory system, it should be possible to obtain information regarding certain aspects of the neural control of ovaluation and menstrual cyclicity in the baboon. Such studies will also provide a comparison of rodent versus primate mechanism, and will yield information to help determine whether data obtained in rodents can be extrapolated in regard to human mechanisms.